The present invention relates to a steering column for a motor vehicle, with a jacket unit in which a steering spindle is supported such that it is rotatable about its steering spindle longitudinal axis, and a bracket unit fixed or fixable on the motor vehicle. The jacket unit is held in or on the bracket unit displaceably in at least one direction parallel and/or transversely to the steering spindle longitudinal axis and securably by a securement mechanism in positions different from one another. The securement mechanism comprises at least one movably, preferably rotatably, bearing-supported securement element, and the jacket unit is secured in at least one locked position of the securement element in its position in or on the bracket unit. In at least one release position of the securement element, the jacket unit is displaceable relative to the bracket unit in at least one of the directions parallel and/or transversely to the steering spindle longitudinal axis.
Generic steering columns are known in a number of physical forms. They are also referred to as adjustable steering columns and permit adjusting the position of the steering wheel in the direction parallel to the steering spindle longitudinal axis and/or carrying out a height adjustment in a direction transversely to the steering spindle longitudinal axis. During driving, the jacket unit is fixed in its position in the bracket unit by means of the securement mechanism. If, by actuating the movably bearing-supported securement element, the securement mechanism is brought into the release position, the jacket unit can be displaced in at least one direction parallel and/or transversely to the steering spindle longitudinal axis relative to the motor vehicle-stationary bracket unit and therewith the position of the steering wheel attached on the steering spindle. When the securement element is subsequently brought again into the locked position, the jacket unit is again held fixedly on the bracket unit. In normal operation, the jacket unit does not move relative to the console unit in the locked position of the securement element. The situation is different in the case in which the motor vehicle collides with another motor vehicle or object. In this case, the steering wheel secured on the steering spindle is not intended to remain rigidly in its position but rather, in the event of an impact of the motor vehicle driver onto the steering wheel, is intended to recede and, for example, be dislocated in the direction toward the engine compartment. In many cases, the kinetic energy of the driver is to be absorbed during this recession. For this purpose, it is known in generic steering columns to lay out the securement mechanism such that it permits a dislocating of the jacket unit relative to the bracket unit even in the locked position of the securement element if, in the event of a collision of the motor vehicle, the motor vehicle driver is thrown onto the steering wheel. In WO 2008/083811 A1 can be found a proposal regarding the manner in which the energy can be absorbed that has been introduced into the steering column through the impact of the motor vehicle driver onto the steering wheel during the dislocating of the jacket unit relative to the bracket unit. The ultimate goal of the energy absorption system disclosed in this publication is dissipating the energy introduced into the steering column during the impact of the motor vehicle driver onto the steering wheel as uniformly as possible and without load peaks, since load peaks or abrupt uncontrolled energy absorptions raise the probability of injuries of the motor vehicle driver.
In the release position of the securement element, a further problematic situation results if the securement mechanism does not secure the jacket unit in position in its relative position to the bracket unit. In this situation, it should be prevented that the jacket unit can be brought into a position relative to the bracket unit in which it can subsequently no longer be secured in the requisite manner or a correct functional use of the steering system by the driver is no longer ensured. In order to delimit the displacement range possible in the release position of the securement element, WO 2008/083811 proposes a break-free element which, upon reaching the maximally permissible displacement range, prevents the jacket unit from becoming further displaced. However, in the event of a correspondingly strong collision the break-free element breaks off and thus enables a further sliding of the jacket unit including the steering spindle such that appropriate energy absorption devices of the steering column can become effective. The disadvantage of this solution is, however, that the breaking away of the break-free element yields a force or load peak which can unnecessarily injure the vehicle driver in the event of a collision. This load peak resulting from the breaking away of the break-free element is generated in the event of a collision in addition to a load peak during the transition from static friction to kinetic friction which results if the jacket unit in the locked position of the securement element, thus with the securement mechanism closed, starts to dislocate relative to the bracket unit.
The present invention addresses the problem of improving a generic steering column to the extent that, on the one hand, the displacement range possible in the release position of the securement element for the jacket unit relative to the bracket unit is limited, on the other hand, unnecessary load peaks are yet as much as possible decreased with respect to prior art.